What could be causing a fuel gauge fault in my Volkswagen Polo?

I would be grateful for your comments regarding the "niggles" I'm having with my 2011 Volkswagen Polo 1.4 Match. On one occasion in July I turned on my ignition only to realise that the display that can show trip/temperature etc was blank. I twiddled the knob at the end of the right hand stick on my steering column and that information returned. Unfortunately not until the end of my journey did I realise that the petrol gauge was not registering. That started to work once I had turned off the ignition then turned it back on. After that I noticed that my petrol gauge was not as accurate as it had been previously. This culminated in August with me travelling 160 miles on a supposedly still full tank.

After some discussion, the VW dealer replaced my fuel gauge sender unit under warranty. For a short time all was well. I knew that if my gauge registered half full then I would put in 20 to 25 litres of petrol. Then I again had problems. I travelled 150 miles on a full tank and then the gauge dropped to 7/8 full. However, when I filled it with petrol I put in 11 litres of petrol and 16 litres on another occasion. I telephoned my garage to express my concerns and agreed to monitor the situation for another two weeks. Last weekend I had a repeat of the display panel/gauge not working. I repeated what I did last time and both showed. I very much feel I would like to have a lot more faith in my fuel gauge and not have to constantly monitor my mileage to determine when I need more fuel.

Asked on 21 December 2013 by AN, Peterborough

Answered by Honest John
I suspect an earthing fault somewhere. Possibly the earth from the instrument cluster to the car body. Fixing that will probably solve both problems. The fuel tank sender replacement may not have been necessary.
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